EXCRETORY PRODUCTS OF MOBILE EPIFAUNA AS A NITROGEN-SOURCE FOR SEAWEEDS

The potential for excretory products of mobile epifauna to be a source of nitrogen for seaweeds was investigated for the fucalean alga Carpo phyllum plumosum var, capillifolium at Matheson Bay: northeastern New Zealand. The epifauna excreted an average of 1.5-2.1 times as much nit rogen as the plants were using. A comparison of rates at which the pla nts took up ammonium with turnover rates of water in the bed indicated that the plants could derive, on average, up to 79% of the nitrogen t hey required for growth from ammonium excreted by epifauna. This value was estimated under the assumption that ammonium excreted by epifauna was instantaneously diluted into the water mass surrounding the entir e bed. In nature, the availability of ammonium to the individual host seaweed should be greater owing to hydrological processes that restric t water Bow around the plant.